Much evidence is available to suggest that there is a reduction in the toxicological potential of Escherishia coli lipopolysaccharide (LPS) after it has undergone heat and chemical detoxification¹. The marker used to measure the change in toxic potency of the molecule was that of an alteration in the ability of LPS to induce changes in responsiveness of both isolated airway smooth muscle and that measured by plethysmography in the guinea pig. The process of detoxification resulted in the removal of the portion of LPS known as lipid A. The hypothesis was formulated that the lipid A portion of LPS was responsible for the major part of the hyperresponsive status of the airway after acute exposure.